Wire for i-shape oil rings and producing method of the same

ABSTRACT

Provided is a wire rod for an I-type oil ring, which includes right and left rail portions and a web portion connecting the rail portions, which has an oil hole or a molten through hole formed in the web portion, and which has a circumscribing circle diameter of 10 mm or less in its transverse contour. The molten through hole has such a remolten portion formed on its exit side as encloses the exit of the molten through hole. The remolten portion exceeds such a molten portion in the transverse section along the center of the molten through hole as is formed in the molten through hole, and is formed to have 200 μm or less from the outer circumference of the molten through hole and 100 μm or less in the depth direction of the molten through hole.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No. 12/663,952filed Dec. 10, 2009, which is a National Stage of InternationalApplication No. PCT/JP2008/060649 filed Jun. 11, 2008, claiming prioritybased on Japanese Patent Application Nos. JP 2007-154000 filed Jun. 11,2007 and JP 2008-089880 filed Mar. 31, 2008, the contents of all ofwhich are incorporated herein by reference in their entirety.

TECHNICAL FIELD

The present invention relates to a wire for I-shape oil rings having aleft and a right rail sections and a web section connecting the left andright rail sections with each other, and a producing method thereof.

BACKGROUND ART

Conventionally, an I-shape wire used for producing oil rings mounted onpistons of internal combustion engines has been provided with oil holesI-shape by stamping. In order to conduct piercing by stamping, it isnecessary to prepare dies corresponding to individual productspecifications.

In contrast, as disclosed in Patent Document 1 (see below), laser beamprocessing has been proposed as means for formation of oil holes in anI-shape oil wire. In order to form oil holes, the technique shown inPatent Document 1 does not need preparing dies corresponding toindividual product specifications, and is advantageous in enablingformation of optional hole shapes and hole pitches by means of laserbeam processing.

The method of producing steel oil rings shown in Patent Document 1 isadvantageous in reduction of man-hour for piercing but involves aproblem that solidified residues (herein below referred to as dross)generated by laser beam processing adhere to a surface of profile wires.When the dross remains, there is a risk that during operation ofengines, the dross exfoliated from the oil rings is mixed in enginelubricant oil as a metal lump thereby damaging a cylinder wall.

In order to improve the influence of dross adhesion, Patent Document 2discloses to use a high thermal energy density processing method(including the YAG laser method) together with an assist gas of oxygenor air, as heating means. Also, the document teaches to reheat the drossand blow out it at a backside of the wire. Patent Document 2 furtherteaches an effectiveness of a method of removing dross in inline bymeans of scrubbing (i.e. grinding, cutting or chipping) as measuresagainst the dross problem.

Patent Document 1: JP-A-3-260473

Patent Document 2: JP-A-9-159025

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

While Patent Document 2 discloses the technique of melting the drossadhered on the surface of the wire to blow out the same with highpressure gas, even if slag is removed from around a hole, there is arisk that the slag adheres again in another location on the surface, orpasses through the hole to adhere to a back surface of the wire, so thatthe technique lacks reliability.

Also, when thermal energy and gas pressure being sufficient to blow outthe dross formed on a through hole are exerted, there is a risk that ashape of the through hole is not conformity with a predetermined shapethereby making the wire to lose a performance as an oil ring.

Accordingly it is an object of the present invention to reduce theinfluence of the dross in a wire for I-shape oil rings and amanufacturing method thereof, and to provide the wire for an I-shape oilring, which wire has oil holes with a predetermined shape anddimensions, and the manufacturing method thereof.

Means for Solving the Problems

The present inventors found out that it is possible to reduce theinfluence of dross and obtain oil holes each having a predeterminedshape by forming a predetermined remelting portion at an outlet side ofeach of the oil holes, which are through holes, formed by melting, of awire for I-shape oil rings.

According to a first aspect of the invention, there is provided:

a wire for I-shape oil rings, comprising a left and a right railsections, and a web section connecting the rail sections with each otherand having oil holes as through holes formed by melting, the wire havinga diameter of not more than 10 mm which is defined by a circlecircumscribing a contour of a cross section of the wire,

wherein there is formed a remelted and solidified portion surrounding anoutlet of each of the through holes,

wherein the remelted and solidified portion is formed so as to exceed amelted and solidified region around the through hole but not to exceed200 μm from the periphery of the through hole, when viewing a crosssection of the wire taken along the axis of the through hole, and

wherein the remelted and solidified portion is formed so as not toexceed 100 μm in a depth direction from the outlet of the through hole.

Preferably, the through holes are formed in a direction from a smalleropening angle side toward a larger opening angle side of the wire whenviewing a cross section of the wire.

Preferably, a height of projections of the through hole on upper andlower surfaces of the wire is not more than 30 μm.

According to a second aspect of the invention, the wire for I-shape oilrings can be produced by the method comprising the steps of:

piercing the through holes by means of laser; and

forming a remelted and solidified portion surrounding an outlet of eachof the through holes by means of laser,

wherein the remelted and solidified portion is formed so as to exceed amelted and solidified region around the through hole but not to exceed200 μm from the periphery of the through hole, when viewing a crosssection of the wire taken along the axis of the through hole, and

wherein the remelted and solidified portion is formed so as not toexceed 100 μm in a depth direction from the outlet of the through hole.

Preferably, the through holes are formed in a direction from a smalleropening angle side toward a larger opening angle side of the wire whenviewing a cross section of the wire.

Preferably, a height of projections of the through hole on upper andlower surfaces of the wire is not more than 30 μm.

Preferably, oil is applied to at least a surface section of the wire forI-shape oil rings, in which surface section a through hole is formed,prior to the piercing process.

Preferably, the piercing process comprises a preliminary piercing stepof piercing a through hole having a smaller size than a predeterminedsize, and a finishing step of piercing a through hole having thepredetermined size.

A surface of the web section formed with the remelted and solidifiedportion may be subjected to shot-blasting after forming the remelted andsolidified portion.

Effect of the Invention

According to the invention, it is possible to reduce the influence ofdross and to obtain an oil hole having a predetermined shape by formingthe remelted and solidified portion on an outlet side of the oil hole,which is the through hole of the wire for I-shape oil rings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a microphotograph showing an example of a surface state of awire for I-shape oil rings, according to the invention;

FIG. 2 is a microphotograph showing an example of a surface state aftera through hole is formed by melting;

FIG. 3 is a schematic view showing an example of the shape of a crosssection of a wire for I-shape oil rings, according to the invention;

FIG. 4 is a schematic view showing an example of a surface state of awire for I-shape oil rings, according to the invention;

FIG. 5 is a photograph showing the microstructure of a cross section ofa wire, according to the invention, after a through hole is formed bymelting;

FIG. 6 is a photograph showing the microstructure of a cross section ofa wire, according to the invention, after a remelted and solidifiedportion is formed;

FIG. 7 is a microphotograph showing a cross section of a wire, accordingto the invention, after forming a through hole by melting;

FIG. 8 is a photograph showing the microstructure of a cross section ofa wire, according to the invention, after forming a remelted andsolidified portion; and

FIG. 9 is a microphotograph showing an appearance of a wire with onesurface side, on which a remelted and solidified portion is formed, andwhich was subjected to shot-blasting.

BEST MODE FOR CARRYING OUT THE INVENTION

With a wire for I-shape oil rings, according to the invention, there isformed a remelted and solidified portion surrounding an outlet of eachof the through holes. The remelted and solidified portion is formed soas to exceed a melted and solidified region around the through hole butnot to exceed 200 μm from the periphery of the through hole, whenviewing a cross section of the wire taken along the axis of the throughhole. Further, the remelted and solidified portion is formed so as notto exceed 100 μm in a depth direction from the outlet of the throughhole.

Dross occurred in the through hole of the wire for I-shape oil rings ismainly produced around the outlet of the through hole 2, that is, aregion which surrounds the outlet in a piercing direction as shown inFIG. 2. According to the invention, since the remelted and solidifiedportion 1 is formed around the outlet of the through hole 2 as shown inFIG. 1, the dross 3 occurred, as shown in FIG. 2, around the outlet ofthe through hole 2 is remelted to be integrated with the wire therebyrestraining the dross from exfoliation resulting in a harmless dross.

The remelted and solidified portion formed on the wire for I-shape oilrings, according to the invention, is required to exceed a melted andsolidified region around the through hole when viewing a cross sectionof the wire taken along an axis of the through hole. Dross is frequentlyformed along a melted and solidified portion formed on the through holeand when the remelting portion does not exceed the melted and solidifiedportion, it is insufficient to inhibit dross from exfoliation and tohave dross made integral with a wire. Also, since there is a risk thatwhen the remelting portion excessively extends, toughness is adverselyaffected, it is preferred that the remelted and solidified portion beformed to have 200 μm or less from the outer circumference of thethrough hole. Also, since there is a risk that when the remelted andsolidified portion is too deep in the depth direction, toughness isadversely affected, it is preferred that the remelted and solidifiedportion be formed to have 100 μm or less in the depth direction of thethrough hole. In addition, the remelted and solidified portion of athrough hole and a thermally affecting layer formed with formation ofthe melting portion are preferably as thin as possible since toughnessis adversely affected thereby.

In the invention, influences of formation of a remelted and solidifiedportion on strength and toughness of a wire is prescribed in terms ofcross section since they are large in a width direction (direction ofwire diameter). When the remelting portion excessively extends in alength direction of a wire, however, there is a risk that strength andtoughness are adversely affected. Accordingly, the remelting portionpreferably has 500 μm or less from the outer circumference of thethrough hole also in the length direction of a wire.

In addition, the through hole is liable to be shaped large on anincidence side of laser and small on an outgoing side. Therefore, aremelted and solidified portion is actually formed on a side, on which athrough hole is small in diameter.

The through holes in the wire for I-shape oil rings, according to theinvention, is preferably formed in a direction from a smaller openingangle side toward a larger opening angle side of the wire when viewing across section of the wire.

When the through holes are formed in the wire for I-shape oil rings,molten metal is occasionally blown off by assist gas. At this time,there is a possibility that flying molten metal (i.e. sputtering)adheres again to the wire. By setting a piercing direction from asmaller opening angle side toward a larger opening angle side of thewire, it is possible to make the wire distant from a scattered region ofsputter, thus enabling reducing a risk that sputter adheres to the wire.In a piercing process, it is preferable to apply assist gas at highpressure of 0.2 MPa or higher in order to blow off a molten metal.

Also, in a remelted and solidified portion forming process, sufficientpressure to blow off dross, used in the piercing process, is not neededbut the use of assist gas at 0.05 MPa or lower is preferable with a viewto having dross remelted and solidified and staying there.

It is preferred that projections on upper and lower surfaces of thethrough hole be 30 μm or less in height. This is because of a risk thatbeing over 30 μm, the projections obstruct oil flow when a wire is usedas an oil ring and of a possibility that the inherent performance of anoil ring is impeded. By making a projection, which is provided on aremelted and solidified portion formed around the through hole, 30 μm orless in height, it is possible to ensure flowability of oil required asa function of an oil ring.

In addition, the height of a projection enables adjusting the injectionpressure of assist gas, a nozzle position, laser power, defocusing, orthe like and exercising control to 30 μm or less while keeping thethrough hole in shape.

A method of manufacturing an I-shape oil ring material, according to theinvention, comprises a piercing process of piercing the through hole bymeans of laser and a remelted and solidified portion forming process offorming a remelted and solidified portion, which encloses an exit of thethrough hole, on an outlet side of the through hole.

While the piercing process and the remelted and solidified portionforming process may be conducted in separate process lines, they arepreferably arranged successively in the same process line since it ispossible to accurately form a remelted and solidified portion around thethrough hole formed in the piercing process and to reduce thepossibility that dross is left.

A method of manufacturing a wire for I-shape oil rings, according to theinvention, preferably comprises an oil applying process, in which oil isapplied to at least a surface of the wire for I-shape oil rings, onwhich a through hole is formed, prior to the piercing process. Byapplying oil to at least a surface of the wire for I-shape oil rings, onwhich a through hole is formed, it is possible to reduce adhesion ofsputter generated in the piercing process. Also, by applying oil also toan outlet side of the through hole, it is possible to use assist gas toreduce adhesion of sputter scattered over an exit surface of the throughhole.

This is because oil applied to the wire prevents sputter from cominginto direct contact with a wire surface.

The piercing process in the invention preferably comprises a preliminarypiercing process of piercing holes each having a smaller dimension thana predetermined dimension, and a finish piercing process of piercingholes each having a predetermined dimension. By piercing through holesby melting in two or more stages, it is possible to reduce drossgenerated in the finish piercing process and a scattering quantity ofsputter.

It is required that holes subjected to piercing in the preliminarypiercing process be shaped to make adhesion of dross and sputter hardand kept in shape, the holes being preferably smaller in length andwidth than holes formed in the finish piercing process. Also, bothcenters of holes being subjected to piercing in the preliminary piercingprocess and holes being subjected to piercing in the finish piercingprocess are preferably present at a width center of the wire.

Penetration is not necessarily required in the preliminary piercingprocess.

In the method of manufacturing a wire for I-shape oil rings, accordingto the invention, that surface of a web section, on which a remelted andsolidified portion is formed, can be subjected to blasting subsequentlyto the remelted and solidified portion forming process. By subjecting asurface, on which a remelted and solidified portion is formed, toblasting, without deformation of the wire, sputter, oil content, etc.adhered on the wire are removed, and it is possible to obtain apredetermined surface roughness. Also, by providing a predeterminedsurface roughness on a surface of a wire for I-shape oil rings,according to the invention, it is possible to expect an improvement in aforce, by which an oil film needed as a function of an oil ring is held.

Also, media, processing pressure, etc. in blasting in the invention canbe appropriately selected according to specifications of a productdepending upon a configuration of adhesion of an object, which adheresto a wire and should be removed.

Example 1

According to the embodiments described above, while a wire for I-shapeoil rings, shown in Specimen 1 in TABLE 1, was caused to runcontinuously, a slot-like oil hole, in which a width 7, a length 8, anda pitch 9 shown in FIG. 4 are indicated in TABLE 1, was formed on a websection of the wire by laser processing, and then a remelted andsolidified portion for making dross harmless was formed by laserprocessing. Details will be described below.

First, in a laser processing equipment used in the invention, an oilapplying process, a preliminary piercing process, a finish piercingprocess, a remelted and solidified portion forming process, and a wetblasting machine were arranged straight along a running line of a wire.For a wire for I-shape oil rings, used in the experiment, a wire, inwhich a width 4, a thickness 5, and a web thickness 6 shown in FIG. 3are indicated in TABLE 1, was prepared, and first, while the wire wascaused to run in a posture, in which a R surface was directed upward asshown in FIG. 3, oil was applied to a surface, on which a through holeof the wire was to be formed.

In the preliminary piercing process, pulse YAG laser having a power of2.0 kW and a smaller spot diameter than that used for piercing of apredetermined dimension was irradiated toward a web from above the Rsurface shown in FIG. 3 for a shorter period of time than that requiredfor piercing of a predetermined dimension in a manner to be focusedapproximately into a web medium point, and nitrogen gases having apressure of 0.7 MPa were jetted to form a smaller through hole than ahole of a predetermined dimension.

In the finish piercing process, pulse YAG laser having a power shown inTABLE 1 and a spot diameter of 0.45 mm was irradiated, as shown in FIG.3, from the upper side, with a round surface having a broader openingangle when viewing a cross section of the wire, toward the web section,for 2 ms so as to be focused approximately on a midpoint of the websection, and simultaneously nitrogen gases having a pressure of 0.7 MPawere jetted to form through holes. At this time, it was confirmed thatwhen only the through hole was formed as shown in FIG. 7, dross 12,partially projecting from a base material and involving the risk ofexfoliation, adhered on an outlet side of the through hole. Also, it wasconfirmed that no sputter adhered to the wire.

Subsequently, pulse YAG laser having a power shown in TABLE 1 wasirradiated to a region covering that portion at an exit of the throughhole, on which dross was generated, for 3.0 ms, and nitrogen gaseshaving a pressure of 0.03 MPa were jetted as assist gas to remelt andsolidify the dross again. The results are shown in FIG. 9 and TABLE 2.In addition, a melted and solidified portion depth shown in TABLE 2 wasmeasured as viewed from a side of the through hole in a direction alonga width 4 of a molten portion.

As shown in FIG. 8 and TABLE 2, a remelted and solidified portion 13 wasformed exceeding a molten portion formed on the through hole in thedirection along the width 4 when viewed in a cross section about acenter of the through hole. In Specimen 1, it was confirmed that theremelted and solidified portion was formed to have 100 μm or less froman outer periphery of an exit of the through hole in the direction alongthe width 4 and 30 μm or less from in a depth direction of the throughhole, that is, a direction along a depth 5. Thereby, it was possible toobtain a wire, in which dross 12 shown in FIG. 7 and having thepossibility of exfoliation as shown in FIG. 7 was remelted andintegrated with a base metal and the risk of dross falling off into anengine was eliminated.

At this time, it was confirmed that a height of a projection in thedirection along the depth 5 was 15 μm at maximum on the outlet side ofthe through hole, that is, on the remelted and solidified portion and 0μm on an incidence side of the through hole, and a periphery of thethrough hole was made smooth. Thereby, it can be expected to ensure oilflowability required as a function of an oil ring.

Subsequently, under the conditions of Specimens 2 to 4 in TABLE 1, awire for I-shape oil rings was caused to run reversely to that in FIG.3, that is, in a posture, in which a rail surface was directed upward,to fabricate a wire for I-shape oil rings going through an oil applyingprocess, a preliminary piercing process, a finish piercing process, anda remelted and solidified portion forming process in the same manner asin Specimen 1. In addition, 10 Cr steel in Specimen 4 shown in TABLE 1and TABLE 2 is one containing, by mass %, 0.5% of C, 0.2% of Si, 0.3% ofMn, 10% of Cr, the balance being Fe, and unavoidable impurities.

In the preliminary piercing process, a wire was caused to run in aposture, in which a R surface was directed upward as shown in FIG. 3,and laser was irradiated toward a web from under a rail surface underthe conditions shown in TABLE 1 to form through holes by melting.

Subsequently, in the finish piercing process, a wire for I-shape oilrings was caused to run in a posture, in which a R surface was directedupward as shown in FIG. 3, and laser was irradiated toward a web from alower side having a smaller opening angle when viewing a cross sectionof the wire, under the conditions shown in TABLE 1 to form throughholes. As a specific example, the results of Specimen 2 are shown inFIG. 5.

It was confirmed that when only a through hole was formed as shown inFIG. 5, dross 10, involving the risk of exfoliation, adhered on anoutlet side of the through hole. Also, at this time, it was confirmedthat sputter did not adhere to the wire.

Subsequently, a wire was caused to run in a posture, in which a Rsurface shown in FIG. 3 was directed upward, and a remelted andsolidified portion was formed at an exit of the through hole under thesame conditions as those in Specimen 1. The results for Specimen 2 areshown in FIG. 6 and TABLE 2, and the results for the rest are shown in alump in TABLE 2. In addition, the respective measurements were made inthe same manner as in Specimen 1.

As shown in FIG. 6 and TABLE 2, it could be confirmed also in Specimens2 to 4 that there was obtained a wire, in which dross 10 was remeltedand integrated with a base material to form a remelted and solidifiedportion 11 and so the risk of dross falling off into an engine waseliminated in the same manner as in Specimen 1.

Example 2

Succeeding the remelted and solidified portion forming process inSpecimen 2 shown in TABLE 1, a wet blasting machine mounted in an inlinemanner was used to subject that surface side of the web, on which aremelted and solidified portion was formed, to blasting of slurry havinga concentration of 20% with a delivery gun under the conditions of awire inbetween distance of 20 mm and air pressure of 0.5 MPa. Theresults are shown in FIG. 9.

As shown in FIG. 9, it was confirmed that oil content was removedwithout marring the shape of a product. At this time, the surfaceroughness of a wire was Rz1.5 μm. Thereby, it is possible to expect animprovement in a force, by which an oil film needed as a function of anoil ring is held.

TABLE 1 CROSS SECTIONAL DIMENSION OF WIRE WIDHT × THICKNESS × DIMENSIONOF HOLE INCIDENCE WEB (INCIDENCE SIDE) SURFACE IN THICKNESS PITCH LENGTHWIDTH PIERCING MATERIAL (mm) (mm) (mm) (mm) PROCESS SPECIMEN 1CORRESPONDING 1.5 × 2.0 × 0.5 5 0.90 0.55 R SURFACE TO SUS420J2 SPECIMEN2 CORRESPONDING 1.5 × 2.0 × 0.5 5 0.90 0.55 RAIL TO SUS420J2 SURFACESPECIMEN 3 CORRESPONDING 1.5 × 1.7 × 0.4 7 1.30 0.50 RAIL TO SUS420J2SURFACE SPECIMEN 4 10Cr STEEL 2.0 × 2.0 × 0.45 5 1.20 0.55 RAIL SURFACEASSIST GAS PRESSURE IN LASER POWER IN ASSIST GAS REMELTED AND LASERREMELTED AND PRESSURE SOLIDIFIED POWER IN SOLIDIFIED IN PORTION PIERCINGPORTION FORMING PIERCING FORMING PROCESS PROCESS PROCESS PROCESS (kW)(kW) (MPa) (MPa) SPECIMEN 1 5.5 0.7 0.7 0.035 SPECIMEN 2 5.5 0.7 0.70.030 SPECIMEN 3 3.5 0.8 0.7 0.025 SPECIMEN 4 5.0 0.7 0.7 0.030 *NOTES:WIRES USED IN SPECIMENS 1 TO 3 CORRESPOND TO JIS SUS420J2

TABLE 2 WIDTH OF DEPTH OF SURFACE DEPTH OF REMELTED REMELTED ROUGH-MELTED AND AND SOLIDIFIED AND SOLIDIFIED HEIGHT OF NESS SOLIDIFIEDPORTION PORTION PORTION BURR OF WEB (μm) (μm) (μm) (μm) (μm) MATERIALMAXIMUM AVERAGE MAXIMUM AVERAGE MAXIMUM AVERAGE MAXIMUM Rz SPECIMENCORRESPONDING 22.8 22.5 75 57 29.2 19.1 15 0.4 1 TO SUS420J2 SPECIMENCORRESPONDING 24.4 22.7 120 110 48.0 47.4 30 1.5 2 TO SUS420J2 SPECIMENCORRESPONDING 15.4 15.3 80 75 48.8 37.7 14 0.4 3 TO SUS420J2 SPECIMEN10Cr STEEL 12.6 11.3 130 120 24.5 23.1 20 0.4 4 * NOTES: WIRES USED INSPECIMENS 1 TO 3 CORRESPOND TO JIS SUS420J2.

DESCRIPTION OF REFERENCE NUMERALS

-   1, 11 and 13: remelted and solidified portions-   2: a through hole formed by melting-   3, 10 and 12: dross-   4: a width-   5: a thickness-   6: a thickness of a web-   7: a width-   8: a length-   9: a pitch of the through holes

What is claimed is:
 1. A method of producing a wire for I-shape oilrings, which wire comprises a left and a right rail sections, and a websection connecting the rail sections with each other, has oil holes asthrough holes formed by melting, and has a diameter of not more than 10mm which is defined by a circle circumscribing a contour of a crosssection of the wire, wherein the method comprises the steps of: piercingthe through holes by means of laser; and forming a remelted andsolidified portion surrounding an outlet of each of the through holes bymeans of laser, wherein the remelted and solidified portion is formed soas to exceed a melted and solidified region around the through hole butnot to exceed 200 μm from the periphery of the through hole, whenviewing a cross section of the wire taken along the axis of the throughhole, and wherein the remelted and solidified portion is formed so asnot to exceed 100 μm in a depth direction from the outlet of the throughhole.
 2. The method of manufacturing a wire for I-shape oil rings,according to claim 1, wherein the through holes are formed in adirection from a smaller opening angle side toward a larger openingangle side of the wire when viewing a cross section of the wire.
 3. Themethod of manufacturing a wire for I-shape oil rings, according to claim1, wherein a height of projections of the through hole on upper andlower surfaces of the wire is not more than 30 μm.
 4. The method ofmanufacturing a wire for I-shape oil rings, according to claim 2,wherein a height of projections of the through hole on upper and lowersurfaces of the wire is not more than 30 μm.
 5. The method ofmanufacturing a wire for I-shape oil rings, according to claim 1,further comprising the step of applying oil to at least a surfacesection of the wire for I-shape oil rings, in which surface section athrough hole is formed, prior to the piercing process.
 6. The method ofmanufacturing a wire for I-shape oil rings, according to claim 1,wherein the step of the piercing comprises a preliminary piercing stepof piercing a through hole having a smaller size than a predeterminedsize, and a finishing step of piercing a through hole having thepredetermined size.
 7. The method of manufacturing a wire for I-shapeoil rings, according to claim 1, wherein after forming the remelted andsolidified portion, a surface of the web section formed with theremelted and solidified portion is subjected to shot-blasting treatment.